Many industrial and commercial processes require the separation of a sludge or slurry into its component liquid and solid. This may be used to treat a sludge or slurry so as to remove a percentage of its liquid, or to produce a liquid with less solid particulate, or both. Some examples of such sludge or slurry to be so treated include sewage, industrial waste, paper pulp or mixtures, whether they be biological, chemical or mineral-based products.
A belt filter system is known which uses two endless belts where one is located fully above the other and each belt is driven so that they will jointly come together downstream from a loading station whereby to capture and compress to remove further liquid from any retained solids.
To assist in liquid draining from the sludge the belts are manufactured from permeable or porous or woven materials and made from materials such as polyester or polypropylene cloth. The belts may also pass around a number of rollers, in a serpentine manner so as to apply increasing pressure to the sludge trapped between the belts.
The two belts are subsequently separated so that remaining compressed solids either falls or is scraped from one or both of the belts. The lower belt is subsequently passed under the device to return to the sludge feed point, whilst the upper belt passes over the device. Liquid sprays are installed on the return section to clean the belts so they do not become blocked with sludge or solids.
One problem with existing belt filters is that when a liquid sludge of low viscosity is fed onto the lower belt which provides an uppermost receiving surface which is substantially horizontal, the sludge may overflow an edge of the belt.
To overcome this problem, some belt filters are provided with pre-dewatering systems, such as de-watering drums, which remove some of the liquid from the sludge or slurry so as to raise its viscosity before placement on the lower belt. Obviously this all adds to the complexity and therefore cost of the process, as well as the overall cost of such belt filters.